Fix #124 Finish implementing command chaining, and make it work for DMD

test/test_command_chain.vader

@@ -0,0 +1,61 @@
+Before:
+  let g:linter_output = []
+  let g:first_echo_called = 0
+  let g:second_echo_called = 0
+  let g:final_callback_called = 0
+
+  function! CollectResults(buffer, output)
+    let g:final_callback_called = 1
+    let g:linter_output = a:output
+    return []
+  endfunction
+  function! RunFirstEcho(buffer)
+    let g:first_echo_called = 1
+
+    return 'echo foo'
+  endfunction
+  function! RunSecondEcho(buffer, output)
+    let g:second_echo_called = 1
+
+    return 'echo bar'
+  endfunction
+
+  call ale#linter#Define('foobar', {
+  \ 'name': 'testlinter',
+  \ 'callback': 'CollectResults',
+  \ 'executable': 'echo',
+  \ 'command_chain': [
+  \   {
+  \     'callback': 'RunFirstEcho',
+  \     'output_stream': 'stdout',
+  \   },
+  \   {
+  \     'callback': 'RunSecondEcho',
+  \     'output_stream': 'stdout',
+  \   },
+  \ ],
+  \})
+
+After:
+  unlet! g:first_echo_called
+  unlet! g:second_echo_called
+  unlet! g:final_callback_called
+  unlet! g:linter_output
+  let g:ale_buffer_info = {}
+  call ale#linter#Reset()
+  delfunction CollectResults
+  delfunction RunFirstEcho
+  delfunction RunSecondEcho
+
+Given foobar (Some imaginary filetype):
+  anything
+
+Execute(Check the results of running the chain):
+  AssertEqual 'foobar', &filetype
+  call ale#Lint()
+  call ale#engine#WaitForJobs(2000)
+
+  Assert g:first_echo_called, 'The first chain item was not called'
+  Assert g:second_echo_called, 'The second chain item was not called'
+  Assert g:final_callback_called, 'The final callback was not called'
+  AssertEqual ['bar'], g:linter_output

test/test_linter_defintion_processing.vader

@@ -1,3 +1,9 @@
+Before:
+  let g:linter = {}
+
+After:
+  unlet g:linter
+
 Execute (PreProcess should throw when the linter object is not a Dictionary):
   AssertThrows call ale#linter#PreProcess('')
   AssertEqual 'The linter object must be a Dictionary', g:vader_exception
@@ -123,3 +129,85 @@ Execute (PreProcess should accept a 'both' output_stream):
   \ 'command': 'echo',
   \ 'output_stream': 'both',
   \})
+
+Execute(PreProcess should complain if the command_chain is not a List):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': 'x',
+  \}
+  AssertThrows call ale#linter#PreProcess(g:linter)
+  AssertEqual '`command_chain` must be a List', g:vader_exception
+
+Execute(PreProcess should complain if the command_chain is empty):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [],
+  \}
+  AssertThrows call ale#linter#PreProcess(g:linter)
+  AssertEqual '`command_chain` must contain at least one item', g:vader_exception
+
+Execute(PreProcess should complain if the command_chain has no callback):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [{}],
+  \}
+  AssertThrows call ale#linter#PreProcess(g:linter)
+  AssertEqual 'The `command_chain` item 0 must define a `callback` function', g:vader_exception
+
+Execute(PreProcess should complain if the command_chain callback is not a function):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [{'callback': 2}],
+  \}
+  AssertThrows call ale#linter#PreProcess(g:linter)
+  AssertEqual 'The `command_chain` item 0 must define a `callback` function', g:vader_exception
+
+Execute(PreProcess should accept a chain with one callback):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [{'callback': 'foo'}],
+  \}
+  call ale#linter#PreProcess(g:linter)
+
+Execute(PreProcess should complain about invalid output_stream values in the chain):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [{'callback': 'foo', 'output_stream': ''}],
+  \}
+  AssertThrows call ale#linter#PreProcess(g:linter)
+  AssertEqual "The `command_chain` item 0 `output_stream` flag must be 'stdout', 'stderr', or 'both'", g:vader_exception
+
+Execute(PreProcess should complain about valid output_stream values in the chain):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [{'callback': 'foo', 'output_stream': 'stdout'}],
+  \}
+  call ale#linter#PreProcess(g:linter)
+  let g:linter.command_chain[0].output_stream = 'stderr'
+  call ale#linter#PreProcess(g:linter)
+  let g:linter.command_chain[0].output_stream = 'both'
+  call ale#linter#PreProcess(g:linter)
+
+Execute(PreProcess should complain about invalid chain items at higher indices):
+  let g:linter = {
+  \ 'name': 'x',
+  \ 'callback': 'x',
+  \ 'executable': 'x',
+  \ 'command_chain': [{'callback': 'foo'}, {'callback': 123}],
+  \}
+  AssertThrows call ale#linter#PreProcess(g:linter)
+  AssertEqual 'The `command_chain` item 1 must define a `callback` function', g:vader_exception